Fusarium head blight in cereals frequently occurs in cases of continuous cloudy weather and light rain, and furthermore high temperature from the heading date to the milk-ripe stage (Yukio Ozeki, Hiroshi Sasaki, Yoichi Amano, Hokkaido no Hatasaku Gijutu (Farming Technology in Hokkaido)—Cereals version—, published by Society for Agricultural Technique Propagation, page 209, 1978), and it is a plant disease which causes great damage to cereals in terms of yields, quality and so forth, and can not be avoided in this country due to the high amount of rainfall during the ripening period. As major pathogenic fungi thereof, Fusarium graminearum, Fusarium culmorum, F. avenaceum and Microdochium nivale have been specified. Although there is difference in occupancy depending on climate conditions and areas, complex infection is often observed in farm fields where the disease has occurred (Kunihei Kishi, Nippon Shokubutsu Byogai Daijiten (Comprehensive Dictionary of Plant Disease in Japan), published by Zenkoku Noson Kyoiku Kyokai (Association for National Farming Village Education), page 74, 1998).
The plant pathogenic fungi which cause this disease produce more than one toxic metabolites referred to as mycotoxin, which contaminates crops during cultivating and poses a risk of ingestion by human and domestic animals through migration to harvestries and processed foods. Researches on mycotoxin in areas such as Europe, North America and East Asia where cultivation of the cereals is active have long history, DON has been specified as a toxic agent whose effects on human and animals are most concerned in terms of both toxicity and the contamination amount, and noticed worldwide. Ingestion of foods contaminated with DON causes acute poisoning where digestive organ symptoms including emesis and diarrhea are major symptoms. In Europe and North America, self-regulating values of DON contamination amount in grains have been established, and the system for intensified surveillance has been organized. While internationally rising momentum in DON surveillance, in 2002 in this country, the Ministry of Health, Labor and Welfare also established an interim standard value of 1.1 ppm for the DON contamination amount in the wheat, and announced that safety of the wheat distributed in the market was assured (Shokuhatu No. 0521001). In relation to the announcement, as an instruction notice for feed safety, the Ministry of Agriculture, Forestry and Fisheries established the interim acceptable value 4.0 ppm for deoxynivalenol in feeds supplied for cattle aged 3 months or more and 1.0 ppm that for domestic animals other than the above (press release). Before DON has been noticed as a fungus producing toxin, people have been protected from healthy risk due to fungous toxin by a law regulation that the contamination ratio of the mixed grains affected with Fusarium head blight shall be made less than 1% by visual check at the shipping stage of crude wheat. Thus, in the production fields of the cereals, the damages with Fusarium head blight have been reduced and inhibited by giving fungicidal agents effective for pathogenic fungi of Fusarium head blight.
Chemicals effective for the pathogenic fungi of Fusarium head blight of the cereals commonly used at present are classified into several groups by their action mechanisms and chemical structures of active ingredients (Agricultural Chemical Handbook, 2001 version, published by Nippon Shokubutsu Boeki Kyokai). The SBI agents characterized by inhibition of biosynthesis of sterol universally present as a component of biological membrane of fungi include (RS)-1-p-chlorophenyl-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)pentan-3-ol (common name: tebuconazole), (1RS,5RS)-5-(4-chlorobenzyl)-2,2-dimethyl-1-(1-H-1,2,4-triazol-1-ylmethyl)cyclopentanol (common name: metconazole), and 1-[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl)-1H-1,2,4-triazole (common name: propiconazole), and they are characterized by having a triazole skeleton in the chemical structures. They have been widely used since they are effective at low doses, rapidly permeate in plant bodies, are resistant to rain and low toxic for flower-visiting insects, and they have a high protection effect on the pathogenic fungi of Fusarium head blight of the cereals. Methyl=(E)-2-{2-[6-(2-cyanophenoxy)pyridine-4-yloxy]phenyl}-3-methoxyacrylate (common name: azoxystrobin) and methyl=(E)-2-methoxyimino[α-(o-tolyloxy)-o-tolyl]acetate (common name: kresoxim-methyl) which were developed as strobilurine derivatives which are anti-mycotic antibiotics and structurally characterised by methoxyacrylate ester are classified into methoxyacrylate type fungicidal agents. The former exerts the protection effect by the inhibition of respiratory activity of the fungi, and the latter does it by the inhibition of cytochrome electron transfer system in mitochondria. The other synthetic fungicidal agents include 1,1′-iminodi(octamethylene)diguanidium=triacetate (common name: iminoctadine acetate). It is considered as the action mechanism that it causes destruction of a membrane lipid bilayer structure of fungi due to a surfactant-like feature derived from its salt structure. Furthermore, the relevance between the pathogenic fungi and drug efficacy has been researched, and it has been demonstrated that the triazole agents are effective for the 3 species of F. graminearum, F. culmorum and F. avenaceum, and that the methoxyacrylate agents are effective for M. nivale. As mentioned above, occurrence of the disease often accompanies mixture of the multiple pathogenic fungi, and thus, the occurrence of the disease has been protected and inhibited by performing rotation spray with taking advantage of characters of respective agents.
Along with attention for DON, as analysis of its contamination concentration has progressed, it has been being demonstrated that there is no direct relevance between an illness degree of the Fusarium head blight and the contamination amount of DON (Bai, G. H., Plattner R and Desjardins A., Relationship between visual scab rating and deoxynivalenol in wheat cultivars, The 1988 National Fusarium Head Blight Forum, Chapter 2, pages 21-25). It has been also demonstrated in recent years that F. graminearum and F. culmorum have DON production capacity but F. avenaceum and M. nivale do not produce DON. It has been reported that when M. nivale is controlled using the methoxyacrylate agent, F. graminearum and F. culmorum which are antagonized are increased resulting in facilitating the increase of DON contamination amount. Thus, the disease protection only by giving the fungicidal agents can not sufficiently prevent the DON contamination. Furthermore, in the production fields of the cereals, even when the Fusarium head blight of the cereals is controlled by combined application of various fungicidal agents, DON is frequently detected at more than 1.1 ppm. This troubles the producers. That is, the DON contamination amount can not be sufficiently reduced only by controlling the pathogenic fungi having a mycotoxin production capacity, which is a conventional technology. Also with respect to fosetyl described in the present statement, the fungicidal effect on the plant pathogenic fungi has been known publicly (U.S. Pat. No. 4,139,616, 1979; and JP 62-87504 A), but there is no mention at all for effects on plants contaminated with mycotoxin. Under such a circumstance, it is an actual state that establishment of a method of substantially reducing the DON contamination amount has been strongly desired in the production fields of the cereals.
The present inventors studied on compositions for agriculture which reduces contamination of wheat with mycotoxin, particularly a DON contamination amount to 1.1 ppm or less or a low contamination amount as possible. As a result, a composition for agri-horticulture developed using one or more compounds A selected from the group consisting of ammonium salts, primary to quaternary ammonium salts, alkali metal salts, alkaline earth metal salts and polyvalent metal salts of phosphorous acid and phosphite ester as an active ingredient(s) has a low controlling effect on pathogenic fungi of Fusarium head blight of the cereals but has an excellent contamination inhibitory effect on a mycotoxin contamination, particularly the DON contamination, and have completed the invention.
Also, the inventors have shown a reduction of the DON contamination amount equal to or less than the standard value in mixed use with a fungicidal agent where DON contamination at high concentration of more than the standard value 1.1 ppm has been observed in the mixed use with fungicidal agent for agri-horticulture, and a further inhibitory effect on the DON contamination amount in the mixed use with a fungicidal agent which originally shows a low contamination level, have found an effect where the DON contamination amount is further reduced compared to a single treatment of a fungicidal agent for agri-horticulture, and have completed the invention.